Delegates from parties supporting Azimio La Umoja began arriving at the KICC as early as 7am for the unveiling of the formation's presidential candidate and coalition structures.
More than 300 delegates from at least 15 parties are expected at the coronation of ODM leader as their presidential candidate.
Security was tight at the entrance of the venue and only invited guests were allowed in.
Guests were screened at two security points and those without invitation cards were turned away.
Journalists were also not spared as they had to produce Media Council of Kenya accreditation cards and national IDs for counterchecking.
Abadare Hall, the venue of the event, was filled with various colours representing the different parties.
It has not been clear whether the running mate will be unveiled as well.
Azimio La Umoja will name its presidential candidate and start campaigns at Jacaranda Grounds in Nairobi later in the day.
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